Electrical enclosures that house circuitry for receiving and distributing electrical power and for otherwise housing various electrical components are well known. For example, in residential and industrial settings, electrical enclosures are used as load centers (e.g., fuse boxes) or electrical disconnects to distribute power from a central power distribution transformer to one or more circuits. These enclosures house fuses, circuit breakers, ground fault interrupters, and other electrical components. In industrial environments, electrical enclosures are used not only for power distribution, but also to house equipment-specific electronics such as fuses, relays, transformers, motor controllers, logic circuitry, power supplies and the like. In general, most any piece of industrial equipment will include a separate enclosure that receives facility power and distributes it in accordance with equipment demands. While the present invention is applicable to most any electrical enclosure, for the sake of brevity it will be discussed with reference to these equipment-specific enclosures.
Electrical enclosures generally comprise a box having an open side or face providing access to the enclosure interior. Mounted within the box are various electrical components as already mentioned above. Electricity is provided to the box by one or more conductors, distributed to the various electrical components therein, and ultimately routed to the specific circuits/conductors that supply the equipment.
During use, the open side of the enclosure is partially or completely covered by a cover panel or door. The panel prevents contact between foreign objects (hands, tools, etc.) and the electrical components within the box. To further protect personnel from potential electrical shock, the panel is designed to prohibit casual opening. That is, it is typically fastened or secured to restrict unauthorized access.
With industrial equipment, it is often necessary to measure the load or current drawn by specific equipment (or specific circuits within the equipment). In fact, facility maintenance personnel often measure current draw of various machines on a periodic basis to determine the operational status or to predict potential problems before they occur. For example, an electric motor will often exhibit a gradual increase or decrease in current draw as the driven equipment wears. By monitoring the current load, technicians can anticipate motor and equipment life and schedule replacement prior to failure. In addition to routine maintenance, current measurement is also used to diagnose malfunctioning equipment.
Of the various devices used to measure electrical current, the hook-on or clamp-on ammeter probably enjoys the most widespread use. Hook-on ammeters of the type having a hook-shaped magnetic core probe that hooks around a current-carrying wire, cable, or conduit are well known. The magnetic core probe of the ammeter reacts with the magnetic field generated by the current flowing through the wire. Since the intensity of the magnetic field is directly proportional to the current, the ammeter may be calibrated to provide an accurate current reading. Hook-on ammeters are often preferred over other current measuring methods as they are simple to use and do not require breaking the wire casing or otherwise contacting the conductor. Nonetheless, hook-on ammeters do require access to the individual conductor.
Unfortunately, in order to access the current-carrying conductors, it is generally necessary to gain access to the enclosure. The same cover panel which was beneficial in preventing unauthorized access to the enclosure now becomes a impediment. Depending on the number of enclosures in a given facility and the frequency with which current measurements are taken, the time spent removing and reinstalling enclosure cover panels can be substantial.
In addition to the time burden of removing the panel, other problems exist. For example, removing the panel may require momentarily shutting down the equipment. This can introduce significant delays in equipment usage depending on the start-up procedure required thereafter. Furthermore, to test current draw, the equipment must be operating. That is, the enclosure is "live" during testing such that the technician is exposed to high voltage conductors. Because of the potential danger involved in dealing with high voltage systems, local or facility regulations may limit enclosure access to licensed electricians.
Still yet another problem experienced by technicians is the isolation of the particular conductor to be measured. Industrial enclosures typically have numerous conductors and, even when the desired conductor is clearly labeled, it must be adequately isolated or separated from the others to permit coupling of the hook-on ammeter.
Accordingly, what is needed is an apparatus for use with an electrical enclosure that permits quick, efficient current measurement of one or more circuits within the enclosure without actually requiring entry therein.